RESTRUCTURING CHARGES (Details 2) - USD ($) $ in Millions	12 Months Ended			21 Months Ended	37 Months Ended	86 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 37.6	$ 112.9	$ 2.7			$ 187.2
Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1.5	76.6	0.5			81.6
Employee severance and job related benefits
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2.0	5.1	0.0			22.9
Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	11.7	15.5	0.9			30.0
Pension and other postretirement benefits curtailment
Restructuring Cost and Reserve [Line Items]
Restructuring charges						4.1
Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.3	2.1	0.6			7.7
Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	22.1	13.6	0.7			40.9
Chlor Alkali Products Becancour
Restructuring Cost and Reserve [Line Items]
Restructuring charges	3.3	0.8	2.0		$ 16.1
Chlor Alkali Products Becancour | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges					3.5
Chlor Alkali Products Becancour | Employee severance and job related benefits
Restructuring Cost and Reserve [Line Items]
Restructuring charges					2.7
Chlor Alkali Products Becancour | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges					4.6
Chlor Alkali Products Becancour | Pension and other postretirement benefits curtailment
Restructuring Cost and Reserve [Line Items]
Restructuring charges					0.0
Chlor Alkali Products Becancour | Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges					0.0
Chlor Alkali Products Becancour | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges					$ 5.3
Chlor Alkali Products and Vinyls Capacity Reductions
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 32.6	111.3		$ 144.0
Chlor Alkali Products and Vinyls Capacity Reductions | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges				78.1
Chlor Alkali Products and Vinyls Capacity Reductions | Employee severance and job related benefits
Restructuring Cost and Reserve [Line Items]
Restructuring charges				5.5
Chlor Alkali Products and Vinyls Capacity Reductions | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges				23.1
Chlor Alkali Products and Vinyls Capacity Reductions | Pension and other postretirement benefits curtailment
Restructuring Cost and Reserve [Line Items]
Restructuring charges				0.0
Chlor Alkali Products and Vinyls Capacity Reductions | Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges				1.7
Chlor Alkali Products and Vinyls Capacity Reductions | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges				$ 35.6
Winchester Segment
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 0.8	$ 0.7			27.1
Winchester Segment | Write-off of equipment and facility
Restructuring Cost and Reserve [Line Items]
Restructuring charges						0.0
Winchester Segment | Employee severance and job related benefits
Restructuring Cost and Reserve [Line Items]
Restructuring charges						14.7
Winchester Segment | Facility exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges						2.3
Winchester Segment | Pension and other postretirement benefits curtailment
Restructuring Cost and Reserve [Line Items]
Restructuring charges						4.1
Winchester Segment | Employee relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges						6.0
Winchester Segment | Lease and other contract termination costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges						$ 0.0